Method of treating paper stock



Patented Dec. 11, 1945 METHOD OF TREATING PAPER STOCK John 0. Dean,Douglaston, and Roy T. Edwards, New York, N. Y., asslgnors toSocony-Vacuum Oil Company, Incorporated, a corporation of New York NoDrawing. Application April 25, 1942,

Serial No. 440,488

4 Claims.

This invention relates to a process for removing ink and pitch frompaper pulp or waste paper in the beater stage.

Many'types of paper are manufactured partially or entirely of wastepaper. This paper, in many instances, has been printed upon withconventional printing inks. Since most inks are black, the presence ofthe pigment tends to throw the reworked stock off-shade to a pronounceddirty gray color. This is frequently objectionable, and for that reason,steps are often taken to remove the ink during the reworking operation.A further objection is that the presence of the ink in the waste papermay complicate subsequent paper making operations. Foaming difiicultiesare frequently encountered, and are often attributed to the presence ofrosin in the printing ink. Expensive foam control measures must then betaken, or the ink must be removed.

Present methods of de-inking are crude and only partially effective. Themost widely used is extraction with kerosene. This solvent is added tothe reworked stock in the beater after it has been thoroughly wet-backand broken down to a uniform pulp. Beating is continued until thesolvent is completely dispersed throughout the pulp. The pulp is thenwashed to remove solvent and ink, but complete removal is impossible dueto the affinity of the pulp for the mixture. The net effect of thismethod is to distribute the ink more uniformly, and also to complicatepaper making by the presence of objectionable kerosene vapors. D

Recourse has been made to the use of emulsi fiers to assist in thisremoval. Attempts have been made to utilize a blend of solvent andemulsifier. Such blends might be termed ,emulsifia'ble solvents, sinceon addition to water an emulsion of solvent in water is formed.Experiments have shown that they are ineffective, due to the fact thatthe droplets of solvent are completely surrounded withwater, and areprevented from mixing with th water-insoluble inks in the pulp.Consequently, ink removal is poor, and in fact, is less than withstraight solvent. An alternate procedure is to add emulsifier to aheater which has been treated with straight solvent. This method is moreeffective than either of the above, but fails chiefly due to theinability of the emulsifler to completely remove solvent and ink whichis firmly bound to the paper fibres. Large quantitles of solvents willscour the pulp satisfactorily, but th cost is prohibitive, and the pulpis softened and thus degraded.

Pitch. removal from virgin pulp is analoy nus to the de-inking of wastepaper. Chemical pulpmaking processes extract considerable quantities ofnaturally occurring resins from the pulp, but in few instances result ina pitch-free stock. For many grades of paper, contamination of thecellulose with small quantities of pitch is not objectionable. Suchinstances include grades sized with from /4,% to 3% or over of rosin.However, in'the manufacture of tissue papers and other unsized orlightly sized grades, pitch is objectionable. It tends to deposit uponthe screens and rolls of the paper machine, and causes imperfectformation and frequent shutdowns for removal. Pitch troubles arecombatted by the addition of solvents, such as de-odorized kerosene, tothe stock to prevent agglomeration of the pitch, or by the use of smallamounts of ahnn 'to set the resin firmly on the fibres.

This invention has for its object the provision of an effective methodcapable of removing ink, pitches, resin, and similar materials frompaper stocks. A particularly important object is the provision of aneffective process for de-inking recovered paper stocks under conditionseconomically permitting the attainment of a high color in the finishedstocks.

This invention is based upon a novel process usinga product applicablefor the de -inking of waste paper and the removal of pitch from paperpulp. The process consists of utilizing a reverse phase emulsion(water-in-oil) to extract the ink, and then causing the emulsion toreverse phase to an oil-in-water emulsion which is easily washed fromthe stock. Such a procedure overcomes the difilculties of the methodsnow in use. The ink is readily extracted, since the product functions asa solvent, and removal after reversion of phase is facilitated becausethe original emulsion carries sufiicient emulsifier to carry both thesolvent and the extracted ink or pitch.

The novel product contains solvent, emulsifier,

and electrolyte, and water. The following materials may b employed insuch a product.

SoZvent.'Any water-immiscible solvent may beemployed, includingpetroleum distillates, coal tar distillates of all types, chlorinatedsolvents such as carbon tetrachloride, orthodichlorobenzene,trichloroethylene, etc. Kerosene is preferred due to its low cost,satisfactory solvent power, and relatively high flash point.

Emulsifier.As emulsifiers, any of the group of soaps, mineral oilsulfonates, esters, glycerides, or the like may be used. Examples aresodium or potassium oleate, sodium salt of a mineral oil Examples I to Vinclusive. With Examples I to V inclusive, the change of phase isaccomplished by added alkali as will be observed later. With Example VI,the alkali required for phase reversal.

is present, but inactiveuntil the change is pro.-

moted by heating.

upon addition of alkali its action is destroyed,

and the emulsion reverses phase. Useful electrolytes include salts ofbivalent and trivalent metals and certain organic acids Examples arealuminum sulfate,potassium sulfate, magnesium sulfate, calcium chloride,ferric or ferrous sulfates, oxalic acid, acetic acid, citric acid,lactic acid, etc.

The treating or de-inking reagent, as applied to the pulp is the reversephase (water-ln-oil), emulsion. Such emulsions are relatively wellknown, and a few examples of such emulsions, particularly suitable forsuch use, follow:

' Water soluble mineral oil sulfonates 2.5 Kerosene 40.0 Epsom salt(magnesium sulfate) 2.0 Water 48.0

Other representative formulae which may be used are as follows:

De-inking and lie-pitching procedure The following procedure is followedin using these emulsions: The stock in the beater, either waste. paperor virgin pulp, is brought to a point where it is thoroughly wet-out anddigested. The

- pulp-'more fibre and less water-is formed. This Example III Weightpercent Oil soluble mineral oil sulfonates -4. 10.0 Kerosene 40.0 Epsomsalt I 1.0 Water 49.0 Example IV v Weight percent Sodium oleate 8.0Carbon tetrachloride 10.0 Kerosene 30.0 Epsomsalt 2.0 Water 50.0EwampleV a Weight percent Mineral oil sulfonates 10.0 Coal tar solventnaphtha (xylol) :50.0 Oxalio acid 1.0 Water 39.0

Example VI V Weight percent Diglycol oleate' 7.0 Kerosene 25.Orthodichlorobenzene 25.0 Trisodium phosphate a. 3.0 Water -40.0

The manufacture of the above emulsion consists essentially of thefollowing The solvent, and emulsifier are mixed in one container;' and.

the water and salt or acid, (electrolyte), in a second. With vigorousagitation the aqueoussolution is added to the solvent solution, andstirring is continued until the product is' made homoeeneous. I

In Example VI a formula is given which is set up on a basis unique ascompared to preceding thus unusual, and since, even with virgin pulp, V

' simply by heating to, a proper degree.

pH of thestock is lowered to below 6.5. A pH of 4.5 is preferred,althoughthis is not essential. At this point the reverse-phase emulsionis added and allowed to mix intimately with the stock. Between 2 and 50gallons of emulsion may be used for one ton of dry pulp, although thepreferred quantity is between 10 and 20 gallons, depending upon thecondition of the pulp to be treated.

For de-inking waste paper, more needed than for the removal of pitch.

After the emulsion has been thoroughly mixed ,emulsion is with the stockand has dissolved the ink or the pitch, the stock is neutralized andrendered slightly alkaline with caustic soda, soda ash, trisodiumphosphate or the like. Any pH above 7.0 is, satisfactory afterneutralization, although a pH of 8.0-8.5 is preferred. The contents ofthe beater may be heated to facilitate the reversion of phase, but thisis not always essential. After the emulsion has reversed completely, itis washed from the stock in the usual manner.

When using a self-reversing emulsion such as that of Example VI, wheresufficient alkali for. phase reversal is incorporated in theformula, butremains inactive untilthe application' of heat, the phase reversal will,of course, be accomplished With the emulsion of Example VI, the phasereversal will be accomplished by heating to aboutlfiflfF. to F,

It will thus be seen that while the process here disclosed'may make useof solvents and emulsi fiers known and presently used for the sameoverall purpose, it makes use of those materials in a new andfar moreeffective way, in that where pitchy materials, (and ink is such a pitchymaterial) must be dissolved, the reagent has a high capability ofreaction in; that "it presents an external phase selectively capable ofattacking the pitch and ink, yet, when it comes'to removing the reagent,it has been converted to a highly water miscible state.

Certain coinmentsare or, interest. The operationmay be conducted eitherin a heater or in a pulp digestor. vantageously-in a pulp digestor. Herea heavier is advantageous in that when the emulsion is inverted by theaddition of alkali'a moreconcem' trated oil-in-water emulsion resultsthan if the operation is conducted in a beater with a less concentratedpulp. The more concentrated emulsions are more stable and are 'moreeasily washed from the pulp..

'In formulae like that of Example VI care" should be taken-not to. usethemwith pulps of very low pH since with such stocks the alkalinity ofthe formula upon heating may not beenough to overcome the acidity ofthestock. Of course, where this condition is. known. to exist, properadjustment of-the electrolyte proportion in the formula can be madetotakecare ofjthe condition. Since most reworked stocks are not It canbe conducted more ad-- when one is removing pitch, the recirculatedwhite water" tends to hold the acidity at optimum levels, this unusualcondition does not often obtain.

In proportioning the amount of emulsion to be used, the concentrationshouldbe adjusted upon the basis of water present in stocks. With beaterstocks, the proportions of 2 to 50 gallons per ton of dry pulp,preferred ranges being -20 gallons per ton should be used, and with moreconcentrated stocks these proportions should be adjusted with regard tothe amount of water present to arrive at water/emulsion ratios of thesame magnitude as those indicated for beater stocks.

We claim:

1. That method for the removal of pitchy materials from paper pulpstocks comprising the steps of contacting the stock while in a digestedand acid condition with an invert emulsion of a solvent for suchpitchymaterial to substantially dissolve the pitchy material therein, thenchanging the phase relationships of the-emulsion and washing theemulsion, containing dissolved pitch, from the stock.

2. That method for the removal of pitchy materials from paper pulpstocks, comprising the steps of admixing with the wet-out, acid, and

, digested stock an emulsion of the water-internal type, comprising awater-immiscible solvent for the pitchy material, an emulsion formingmaterial, and an emulsion inverting electrolyte inactive under alkalineconditions, dissolving and removing said pitchy materials by the use ofsaid invert emulsion, then causing reversion of the emulsion to awater-external typ and washing the emulsion and contained pitchymaterial from the pulp stock.

3. That method for the removal of pitchy materials from paper stockscomprising bringing the stock to a hydrogen ion concentrationof belowabout 6.5, adding thereto a water-intemal type.

of emulsion comprising a solvent agent for the pitchy material,substantially removing said pitchy material from said stock by the useof said emulsion then bringing about reversion of the emulsion to thewater-external type, and removing said emulsion and contained pitchymaterial from said-stock.

4. That method for the removal of pitchy materials from paper stockscomprising bringing the stock to a digested and acid condition, addingthereto a water-in-oil emulsion stable under acidic conditions andagitating it with the stockv to dissolve and remove pitchy materialtherefrom, then bringing the stock to an alkaline condition andinverting the emulsion to an oil-internal condition and washing theemulsion from the stock.

JOHN C. DEAN.

